Optical devices used in communications applications often have a light-transmitting medium positioned on a base. Optical gratings for separating light signals of different wavelengths are often formed in the light-transmitting medium. Waveguides for guiding the light signals can also be defined in the light-transmitting medium. A first portion of these waveguides can serve as input waveguides that carry the light signals to the optical grating and a second portion of these waveguides can serve as output waveguides that carry the separated light signals away from the optical grating. In order to reduce optical loss and cross-talk, the waveguides and the optical grating must be precisely aligned.
The waveguides and the optical grating are often defined by surfaces that are etched into the light transmitting medium. However, these surfaces must often be etched to different depths. As a result, the surfaces are often formed in series. For instance, surfaces that define the waveguides can be formed before or after surfaces that define the grating. However, in order to keep the precise alignment between the waveguides and the grating, the sequentially formed surfaces also must be precisely aligned. The difficulty in achieving alignment between sequentially formed surfaces is a source of optical loss in these devices.
For the above reasons, there is a need for an improved method of fabricating surfaces of these optical devices to different depths.